FitzGerald J., Dennis A., Durcikova A. Business Data Communications and Networking

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7.3 BACKBONE NETWORK ARCHITECTURES 255

7.2 VLANs IN SHANGRI-LA

MANAGEMENT

FOCUS

Shangri-La’s Rasa Sayang Resort and Spa is a

5-star luxury resort hotel located on the scenic

Batu Feringgi Beach in Penang, Malaysia. The

resort has two main buildings, the 189-room Gar-

den Wing and the 115-room Rasa Wing, with

additional 11 private spa villas.

Over the years, the resort had installed three

separate networks: one for the resort’s opera-

tions, one for its POS (point-of-sales) system, and

one for Internet access for guests (which was

wired, not wireless). The networks were separate

to ensure security, so that users of one network

could not gain access to another.

As part of multimillion dollar renovation, the

resort decided to upgrade its network to gigabit

speeds and to offer wireless Internet access to

its guests. Rather than build three separate net-

works again, it decided to build one network using

VLANs. The resort installed 12 wireless access

points and 24 VLAN switches, plus two larger

core VLAN switches. The VLAN architecture pro-

vides seamless management of the wired and

wireless components as one integrated network,

and ensures robust performance and security.

SOURCE: Source: ‘‘Wireless Access Amidst Lush

Greenery of Penang Shangri-La’s Resort,’’ HP

ProCurve Customer Case Study, Hewlett-Packard,

2010.

switches] would ignore QoS information.) With the Ethernet packet’s ability to carry

VLAN information that includes priorities, we now have QoS capabilities in the data

link layer. This means we can connect VOIP telephones directly into a VLAN switch

and conﬁgure the switch to reserve sufﬁcient network capacity so that they will always

be able to send and receive voice messages.

The biggest drawbacks to VLANs are their cost and management complexity.

VLAN switches also are much newer technologies that have only recently been stan-

dardized. Such “leading-edge” technologies sometimes introduce other problems that

disappear only after the speciﬁc products have matured.

How VLANs Work VLANs work somewhat differently than the traditional

Ethernet/IP approach described in the previous chapters. Each computer is assigned

into a speciﬁc VLAN that has a VLAN ID number (which ranges from 1 to 1005 or

to 4094 depending on whether the extended range standard is used). Each VLAN ID

is matched to a traditional IP subnet, so each computer connected to a VLAN switch

also receives a traditional IP address assigned by the VLAN switch (the switch acts as

a DHCP server; see Chapter 5). Most VLAN switches can support only 255 separate

VLANs simultaneously, which means each switch can support up to 255 separate IP

subnets, which is far larger than most organizations want in any single device.

Computers are assigned into the VLAN (and the matching IP subnet) based on the

physical port on the switch into which they are connected.

Don’t confuse the physical

port on the switch (which is the jack the cable plugs into) with the TCP port number

from Chapter 5; they are different—it’s another example of networking using the same

One type of VLAN switches used to enable computers to be assigned into VLANs is based on dynamic

criteria such as their Ethernet address, but this type of switch has essentially disappeared. The extra cost of

dynamic VLAN switches outweighed the beneﬁts they provided and they lost in the marketplace.

256 CHAPTER 7 BACKBONE NETWORKS

word (“port”) to mean two different things. The network manager uses software to assign

the computers to speciﬁc VLANs using their physical port numbers so it is simple to

move a computer from one VLAN to another.

When a computer transmits an Ethernet frame, it uses the traditional Ethernet and

IP addresses we discussed in previous chapters (e.g., Chapters 4 and 5) to move the

frame through the network because it doesn’t know that it is attached to a VLAN switch.

Recall that as a message moves through the network, the IP address is used to specify

the ﬁnal destination and the Ethernet address is used to move the message from one

computer to the next along the route to the ﬁnal destination. Some devices, such as

layer-2 switches, are transparent; the Ethernet frame passes through them unchanged.

Other devices, such as routers, remove the Ethernet frame and create a new Ethernet

frame to send the message to the next computer. VLANs are transparent—although they

do change the frame at times.

Let’s use Figure 7.13 to explain how VLAN switches work. We’ll assume this

network uses the ﬁrst three bytes to specify the IP subnet. In this example, we have

three VLAN switches with three IP subnets (179.58.10.x, 179.58.3.x, and 179.58.11.x)

and three VLANs (10, 20, 30). A router is used to enable communication among the

different IP subnets.

Suppose a computer connected to switch 2 (IP 179.58.10.102) sends a message to

a c omputer on the same IP subnet that is also connected to switch 2 (IP 179.58.10.103).

The sending computer will recognize that the destination computer is in the same IP

subnet, create an Ethernet frame with the destination computer’s Ethernet address (using

ARP if needed to ﬁnd the Ethernet address), and transmit the frame to VLAN switch

2. When a VLAN switch receives a frame that is destined for another computer in the

same subnet on the same VLAN switch, the switch acts as a traditional layer-2 switch:

it forwards the frame unchanged to the correct computer. Remember from Chapter 6

that switches build a forwarding table that lists the Ethernet address of every computer

connected to the switch. When a frame arrives at the switch, the switch looks up the

Ethernet address in the forwarding table, and if it ﬁnds the address, then it forwards the

frame to the correct computer. We discuss what happens if the Ethernet address is not

in the forwarding table in a moment.

Suppose that a computer wants to send a message to a computer in the same subnet,

but that the destination computer is actually on a different VLAN switch. For example

in Figure 7.13, suppose this same computer (IP 179.58.10.102) sends a message to a

computer on switch 3 (179.58.10.50). The sending computer will act exactly the same

because to it, the situation is the same. It doesn’t know where the destination computers

is; it just knows that the destination is on its own subnet. The sending computer will

create an Ethernet frame with the destination computer’s Ethernet address (using ARP if

needed to ﬁnd the Ethernet address) and transmit the frame to VLAN switch 2. Switch

2 receives the frame, looks up the destination Ethernet address in its forwarding table,

and recognizes that the frame needs to go to switch 3.

Virtual LAN switches use Ethernet 802.1q tagging to move frames from one switch

to another. Chapter 4 showed that the layout of an Ethernet frame contains a VLAN tag

ﬁeld which VLAN switches use to move frames among switches. When a VLAN switch

receives an Ethernet frame that needs to go to a computer on another VLAN switch, it

changes the Ethernet frame by inserting the VLAN ID number and a priority code into the

VLAN tag ﬁeld. When a switch is conﬁgured, the network administrator deﬁnes which

7.3 BACKBONE NETWORK ARCHITECTURES 257

VLANs span which switches and also deﬁnes VLAN trunks—circuits that connect two

VLAN switches and enables trafﬁc to ﬂow from one switch to another. As a switch

builds its forwarding table, it receives information from other switches and inserts the

Ethernet addresses of computers attached to them into its forwarding table along with

the correct trunk to use to send frames to them.

In this case, switch 2 receives the frame, and uses the forwarding table to identify

that it needs to send the frame over the trunk to switch 3. It changes the frame by inserting

the VLAN ID and priority code into the tag ﬁeld and transmits the frame over the trunk

to switch 3. Switch 3 receives the frame, looks the Ethernet address up in its forwarding

table, and identiﬁes the speciﬁc computer the frame needs to be sent to. The switch

removes the VLAN tag information and transmits the revised frame to the destination

computer. In this way, neither the sending computer nor the destination computer are

aware that the VLAN exists. The VLAN is transparent.

Suppose the same sending computer (179.58.10.102) wants to send a message to a

computer on a different subnet in the same VLAN (e.g., 179.58.7.30 on the same switch

or 179.58.11.20 on switch 3). The sending computer recognizes that the destination is

on a different subnet, and therefore creates an Ethernet frame with a destination Ethernet

address of its router (179.58.10.1), and sends the frame to switch 2.

At this point, everything works the same as in the previous example. Switch 2 looks

up the destination Ethernet address in its forwarding table, and recognizes that the frame

needs to go to switch 1 because the router’s Ethernet address is listed in the forwarding

table as being reachable through switch 1. Switch 2 sets the VLAN tag information and

sends the frame over the trunk to switch 1. Switch 1 looks up the destination Ethernet

address in its forwarding table, and sees that the router is attached to it. Switch 2 removes

the VLAN tag ﬁeld and sends the frame to the router.

The router is a layer-3 device, so when it receives the message, it strips off the

Ethernet frame and reads the IP packet. It looks in its routing table and sees that the

destination IP address is within a subnet it controls (either 179.58.7.x or 179.58.11.x

depending on which destination computer the packet was sent to). The router creates a

new Ethernet frame and sets the destination Ethernet address to the destination computer

(using an ARP if needed) and sends the frame to switch 1.

Switch 1 reads the Ethernet address and looks it up in its forwarding table. It discovers

the frame needs to go to switch 2 (for 179.58.7.30) or switch 3 (for 179.58.11.20), sets the

VLAN tag ﬁeld, and forwards the frame over the trunk to the correct switch. This switch

in turn removes the VLAN tag information and sends the frame to the correct computer.

Until now, we’ve been talking about unicast messages—messages from one com-

puter to another—that are the majority of network trafﬁc. However, what about broadcast

messages such as ARPs that are sent to all computers in the same subnet? Each com-

puter on a VLAN switch is assigned into a subnet with a matching VLAN ID. When

a computer issues a broadcast message, the switch identiﬁes the VLAN ID of the sending

computer and then sends the frame to all other computers that have the same VLAN ID.

These computers may be on the same switch, or on different switches. For example, sup-

pose computer 179.58.10.102 issues an ARP to ﬁnd an Ethernet address (e.g., the router’s

address). Switch 2 would send the broadcast frame to all attached computers with the

same VLAN ID (e.g., 179.58.10.103). Switch 2’s trunking information also tells it than

VLAN 10 spans switch 1 and switch 3, so it sends the frame to them. They, in turn,

use their tables to send it to their attached computers that are in the same VLAN (which

258 CHAPTER 7 BACKBONE NETWORKS

includes the router). Note that the router has multiple IP addresses and VLAN IDs because

it is connected to several different VLANs and subnets (three, in our example here).

We have also assumed that the VLAN switch has a complete forwarding table—a

table that lists all the Ethernet addresses of all the computers in the network. Just like

a layer-2 switch, the VLAN switch learns Ethernet addresses as it sends and receives

messages. Where the VLAN switch is ﬁrst turned on, the forwarding table is empty, just

like the forwarding table of a layer-2 switch; however, its VLAN ID and trunk tables are

complete because these are deﬁned by the network administrator. Suppose the switch has

just been turned on and has an empty forwarding table. It receives an Ethernet frame,

looks up the destination address in the forwarding table, and does not ﬁnd where to send

it. What happens?

If the VLAN switch were a layer-2 switch, it would send the frame to all ports.

However, a VLAN switch can be a bit smarter than this. If you think about how IP

works, you will see that an Ethernet frame is always sent to a computer in the same IP

subnet as the sending computer. Any time a frame needs to move to a different subnet, it

goes through a router which sits on both subnets. Think about it for a minute before you

continue reading. Therefore, any time the VLAN switch can’t ﬁnd a destination Ethernet

address in the forwarding table, it treats the frame as a broadcast frame and sends it to

all the computers in the same subnet, which in VLAN terms means all the computers

with the same VLAN ID.

This means that a VLAN architecture can improve performance by reducing trafﬁc

in the network compared with a switched backbone architecture. Since a switched back-

bone uses layer-2 switches, all the computers are in the same subnet, and all broadcast

trafﬁc goes to all computers. By using a VLAN we can limit where broadcast trafﬁc

ﬂows by dividing the network into separate subnets, so that broadcast messages only go

to computers in the same subnet.

7.4 THE BEST PRACTICE BACKBONE DESIGN

The past few years have seen radical changes in the backbone, both in terms of new tech-

nologies (e.g., gigabit Ethernet) and in architectures (e.g., switched backbones, VLANs).

Fifteen years ago, the most common backbone architecture was the routed backbone,

connected to a series of shared 10Base-T hubs in the LAN.

Today, the most effective architecture for the distribution layer in terms of cost

and performance is a switched backbone (either rack-mounted or using a chassis switch)

because it provides the best performance at the least cost. For the core layer, most

organizations use a routed backbone. Many large organizations are now implementing

VLANs, especially those which have departments spread over multiple buildings, but

VLANs add considerable cost and complexity to the network.

Given the trade-offs in costs, there are several best practice recommendations. First,

the best practice architecture is a switched backbone or VLAN for the distribution layer

and a routed backbone for the core layer. Second, the best practice recommendation

for backbone technology is gigabit Ethernet. Considering the LAN and backbone envi-

ronments together, the ideal network design is likely to be a mix of layer-2 and layer-3

7.4 THE BEST PRACTICE BACKBONE DESIGN 259

Distribution

Access

Layer-2 or

Layer-3

Switch

Layer-2

Switch

Building Building Building

Core

Layer-3 Switching

FIGURE 7.14 The best practice network design

Ethernet switches. Figure 7.14 shows one likely design. The access layer (i.e., the LANs)

uses 100Base-T layer-2 Ethernet switches running on cat 5e or cat 6 twisted-pair cables

to provide ﬂexibility for 100Base-T or 1000Base-T. The distribution layer uses layer-2

or layer-3 Ethernet switches that use 100Base-T or more likely 1000Base-T/F (over ﬁber

or cat 6) to connect to the access layer. To provide good reliability, some organizations

may provide redundant switches, so if one fails, the backbone continues to operate. The

core layer uses layer-3 Ethernet switches running 10 GbE or 40 GbE over ﬁber.

7.1 MULTIPROTOCOL LABEL SWITCHING

TECHNICAL

FOCUS

Multiprotocol Label Switching (MPLS) is an

approach to improving QoS and the movement

of packets with different layer-2 protocols through

TCP/IP networks.

With MPLS, routers called Label Switched

Routers (LSRs) are used. The network manager

deﬁnes a series of Forwarding Equivalence Classes

(FEC) through the network of LSRs. Each FEC has a

reserved data rate and a QoS.

When a packet arrives at the edge of the MPLS

network, an edge LSR reads the destination address

on the incoming packet. The edge LSR can be con-

ﬁgured to use the IP address, the IP address and the

source or destination port, or the address in any pro-

tocol understood by the LSR. The edge LSR accepts

the incoming packet and attaches an MPLS

label

packet that contains the FEC address). The edge LSR

then forwards the packet to the next LSR as deﬁned

in the FEC.

This LSR reads the MPLS label and removes it

from the incoming packet, consults its MPLS address

table to ﬁnd the packet’s next destination, attaches

a new MPLS label with the new FEC address, and

forwards the packet to the next LSR in the FEC.

This process continues until the packet reaches

the edge LSR closest to its ﬁnal destination. This

edge LSR strips off the MPLS label and forwards

the packet outside of the MPLS network in exactly

the same format in which it entered the MPLS

network.

The advantage of MPLS is that it can easily inte-

grate layer-2 protocols and also provide QoS in an IP

environment. It also enables trafﬁc management by

enabling the network manager to specify FEC based

on both the IP address and the source or destination

port.

260 CHAPTER 7 BACKBONE NETWORKS

7.5 IMPROVING BACKBONE PERFORMANCE

The method for improving the performance of BNs is similar to that for improving

LAN performance. First, ﬁnd the bottleneck, then solve it (or, more accurately, move

the bottleneck somewhere else). You can improve the performance of the network by

improving the performance of the computers and other devices in the network, by upgrad-

ing the circuits between computers, and by changing the demand placed on the network

(Figure 7.15).

7.5.1 Improving Computer and Device Performance

The primary functions of computers and devices in BNs are routing and protocol transla-

tions. If the devices and computers are the bottleneck, routing can be improved with faster

devices or a faster routing protocol. Distance vector routing is faster than dynamic routing

(see Chapter 5) but obviously can impair circuit performance in high-trafﬁc situations.

Link state routing is usually used in WANs and MANs because there are many possible

routes through the network. BNs often have only a few routes through the network, so

link state routing may not be too helpful since it will delay processing and increase the

network trafﬁc because of the status reports sent through the network. Distance vector

routing will often simplify processing and improve performance.

Most backbone devices are store-and-forward devices. One simple way to improve

performance is to ensure that they have sufﬁcient memory. If they don’t, the devices will

lose packets, requiring them to be retransmitted.

7.5.2 Improving Circuit Capacity

If network circuits are the bottlenecks, there are several options. One is to increase overall

circuit capacity (e.g., by going from 100Base-T Ethernet to gigabit Ethernet). Another

option is to add additional circuits alongside heavily used ones so that there are several

circuits between some devices.

Performance Checklist

Increase Computer and Device Performance

• Change to a more appropriate routing protocol (either distance vector or link state)

• Buy devices and software from one vendor

• Increase the devices' memory

Increase Circuit Capacity

• Upgrade to a faster circuit

• Add circuits

Reduce Network Demand

• Change user behavior

• Reduce broadcast messages

FIGURE 7.15

Improving backbone

network performance

7.6 IMPLICATIONS FOR MANAGEMENT 261

In many cases, the bottleneck on the circuit is only in one place—the circuit to the

server. A switched network that provides 100 Mbps to the client computers but a faster

circuit to the server (e.g., 1000Base-T) can improve performance at very little cost.

7.5.3 Reducing Network Demand

One way to reduce network demand is to restrict applications that use a lot of network

capacity, such as desktop videoconferencing, medical imaging, or multimedia. In practice,

it is often difﬁcult to restrict users. Nonetheless, ﬁnding one application that places a

large demand on the network and moving it can have a signiﬁcant impact.

Much network demand is caused by broadcast messages, such as those used to

ﬁnd data link layer addresses (see Chapter 5). Some application software packages and

NOS modules written for use on LANs also use broadcast messages to send status

information to all computers on the LAN. For example, broadcast messages inform users

when printers are out of paper, or when the server is running low on disk space. When

used in a LAN, such messages place little extra demand on the network because every

computer on the LAN gets every message.

This is not the case for routed backbones because messages do not normally ﬂow

to all computers, but broadcast messages can consume a fair amount of network capacity

in switched backbones. In many cases, broadcast messages have little value outside their

individual LAN. Therefore, some switches and routers can be set to ﬁlter broadcast

messages so that they do not go to other networks. This reduces network trafﬁc and

improves performance.

7.6 IMPLICATIONS FOR MANAGEMENT

As the technologies used in LANS and WLANs become faster and better, the amount

of trafﬁc the backbone network needs to support is increasing at an even faster rate.

Coupled with the signiﬁcant changes in the best practice recommendations for the design

of backbone networks, this means that many organizations have had to replace their

backbones completely. We would like to think that these have been one-time expenditures,

but, as trafﬁc grows, demand placed on the backbone will continue to increase meaning

the amount spent on switches and routers for use in the backbone will increase. Designing

backbone networks to be easily upgradable is now an important management goal.

As recently as ﬁve years ago, ATM was seen as a viable technology for use in

backbone networks (ATM is discussed in the next chapter). Today, however, it is clear

that Ethernet has beaten ATM as the best backbone technology and ATM is now a

legacy backbone technology: no new backbone networks will be installed using it and

most vendors have stopped the development of ATM for backbone networks.

As Ethernet moves more extensively into the backbone, the costs associated with

buying and maintaining backbone devices and training networking staff will decrease,

since now there will be one standard technology in use throughout the LAN, WLAN,

and backbone. The new focus is on faster and faster versions of Ethernet. While we will

spend more on new equipment, performance will increase much more quickly, and the

cost to operate the equipment will decrease.

262 CHAPTER 7 BACKBONE NETWORKS

SUMMARY

Network Components There are two basic components to a BN: the network cable and the

hardware devices that connect other networks to the backbone. The cable is essentially the same as

those used in LANs, except that it is usually ﬁber optic to provide higher data rates. The hardware

devices include routers, gateways, and switches. Switches connect two LAN segments that use the

same data link and network protocol and forward only those messages that need to go to other

network segments. Routers connect two or more LANs that use the same or different data link

protocols but employ the same network protocol. Gateways connect two or more LANs that use the

same or different data link and network protocols (usually different). Layer-2 switches are similar

to bridges, whereas layer-3 switches are similar t o routers.

Backbone Architectures Network designers often think about three distinct technology layers

when designing backbones. The access layer is the LAN, the distribution layer connects the LANs

together, and the core layer connects the distribution-layer BNs together. The distribution layer

is usually a backbone within a building, whereas the core layer often connects buildings and is

sometimes called the campus network. A routed backbone uses a set of routers or layer-3 switches

to connect LANs together and moves messages using layer-3 addresses. A switched backbone

uses one device, usually a layer-2 switch, to connect the LANs. A VLAN uses layer-2 or layer-3

switches to build logical or virtual LANs that enable the network manager to assign capacity

separate from physical location.

Best Practice Backbone Design The best practice backbone architecture for most organizations

is a switched backbone (using a rack or a chassis switch) or VLAN in the distribution layer and a

routed backbone in the core layer. The recommended technology is gigabit Ethernet.

Improving Backbone Performance Backbone performance can be improved by choosing the best

network layer routing protocols. Upgrading to faster circuits and adding additional circuits on very

busy backbones can also improve performance. Finally, one could move servers closer to the end

users or reduce broadcast trafﬁc to reduce backbone trafﬁc.

KEY TERMS

access layer

backbone network (BN)

campus network

chassis switch

core layer

distribution layer

enterprise network

forwarding equivalence

class (FEC)

gateways

IEEE 802.1q

label switched router

(LSR)

layer-2 switch

layer-3 switch

main distribution facility

(MDF)

module

multiprotocol label

switching (MPLS)

multiswitch VLAN

patch cables

rack

routed backbone

router

single-switch VLAN

switched backbone

virtual LAN (VLAN)

VLAN ID

VLAN tag

VLAN trunk

QUESTIONS

1. Compare and contrast switches, routers,

and gateways.

2. How does a layer-2 switch differ from

a layer-3 switch?

3. How does a router differ from a layer-3 switch?

4. Under what circumstances would you

want to use a router?

EXERCISES 263

5. What is an enterprise network?

6. What are the three technology layers impor-

tant in backbone design?

7. Explain how routed backbones work.

8. Where are routed backbones most

commonly used?

9. Explain how switched backbones work.

10. What are the key advantages and disadvantages

of routed and switched backbones?

11. Compare and contrast rack-based and

chassis-based switched backbones.

12. What is a module and why are mod-

ules important?

13. Explain how single-switch VLANs work.

14. Explain how multiswitch VLANs work.

15. What is IEEE 802.1q?

16. What are the advantages and disad-

vantages of VLANs?

17. How can you improve the performance of a BN?

18. Why are broadcast messages important?

19. What are the preferred architectures used in the

technology layers in backbone design?

20. Some experts are predicting that Ethernet will

move into the WAN. What do you think?

EXERCISES

7-1. Survey the BNs used in your organization. Do they

use Ethernet or some other technology? Why?

7-2. Document one BN in detail. What devices are

attached, what cabling is used, and what is the topol-

ogy? What networks does the backbone connect?

7-3. You have been hired by a small company to install

a backbone to connect four 100base-T Ethernet

LANs (each using one 24-port hub) and to pro-

vide a connection to the Internet. Develop a sim-

ple backbone and determine the total cost (i.e.,

select the backbone technology and price it, select

the cabling and price it, select the devices and

price them, and so on). Prices are available at

www.datacommwarehouse.com, but use any source

that is convenient. For simplicity, assume that cat-

egory 5, category 5e, category 6, and ﬁber-optic

cable have a ﬁxed cost per circuit to buy and install,

regardless of distance, of $50, $60, $120, and $300,

respectively.

MINI-CASES

I. Pat’s Engineering Works

Pat’s Engineering Works is a small company that specializes in complex engineering consulting projects. The

projects typically involve one or two engineers who do data intensive analyses for companies. Because so much

data are needed, the projects are stored on the company’s high-capacity server but moved to the engineers’

workstations for analysis. The company is moving into new ofﬁces and wants you to design its network. It has

a staff of 8 engineers (which is expected to grow to 12 over the next 5 years), plus another 8 management and

clerical employees who also need network connections but whose needs are less intense. Design the network.

Be sure to include a diagram.

II. Hospitality Hotel

Hospitality Hotel is a luxury hotel whose guests are mostly business travelers. To improve its quality of service,

it has decided to install network connections in each of its 600 guest rooms and 12 conference meeting rooms.

Last year, the hotel upgraded its own internal networks to switched 100Base-T, but it wants to keep the public

network (i.e., the guest and meeting rooms) separate from its private network (i.e., its own computer systems).

Your task is to design the public network and decide how to connect the two networks together. Be sure to

include a diagram.

264 CHAPTER 7 BACKBONE NETWORKS

III. Indiana University

Reread Management Focus 7.1. What other alternatives do you think that Indiana University considered? Why

do you think they did what they did?

IV. Shangi-La

Reread Management Focus 7.2. What other alternatives do you think that the Shangri-La Resort considered?

Why do you think they did what they did?

V. Western Trucking

Western Trucking operates a large ﬂeet of trucks that deliver shipments for commercial shippers such as

food stores, retailers, and wholesalers. Their main headquarters building and secondary building are shown in

Figure 7.16. They currently have a mix of shared 10base-T and switched 10base-T LANs, connected by a

series of switches. They want to upgrade to a faster network. Design a new network for them, including the

architecture and speciﬁc backbone and LAN technologies to be used.

Data

Processing

Accounts

Payable

and Payroll

Accounts

Receivable

Sales and

Marketing

Security

President's

office

Conference

room

Intrastate

Operations

Interstate

Operations

Agent

operations

Customer

Service

Mail

room

Human

Resources

Information

Services

Fleet Maintenance

Dispatch

Lobby

and

reception

Main building

Secondary building

Parking lot

FIGURE 7.16 Facility map of the Western Trucking headquarters